Our long-term objective is to enhance the effectiveness of early treatment for OEF/OIF veterans suffering from combat-related PTSD;and alcohol abuse by advancing knowledge on models and mechanisms that explain the association between PTSD symptoms and alcohol use. Research has shown high comorbidity rates between PTSD and alcohol use disorders (AUDs) among combat exposed veterans. While prior research studies have identified patterns consistent with social learning (SLT) and self-medication perspectives (SM), they are limited by a reliance on static assessments of symptoms and alcohol use over long time intervals and retrospective reports. SLT/SM models reflect rapid unfolding of internal processes and behaviors over time, often within a day, and require methods that can measure this potentially proximal interplay of symptom changes and alcohol use. Ecological momentary assessment (EMA) is a method that can capture near real time day-to-day symptoms and behaviors in a participant's natural environment. Using EMA, the objectives of the proposed study are to: (1) examine relations between combat-related PTSD and alcohol use over time among OEF/OIF veterans;(2) test theorized (Self-Medication/Social Learning Theory) PTSD and alcohol use associations (cognitive mediation, coping, social influences);(3) examine effect of length of time post-deployment on PTSD and alcohol use associations;and (4) examine associations between SM and concurrent functioning. A total of 168 OEF/OIF veterans who have combat related partial or full PTSD and endorse risky drinking behavior, will receive cell phones that are connected to an Interactive Voice Response (IVR) system. The IVR system will provide daily prompts to participants to report on PTSD and alcohol use for 28 days in their natural environments. In person clinical interviews will be conducted at baseline and immediately following the completion of the IVR protocol. This research will yield a rich dataset, and findings will offer important implications for interventions. Results will help guide front-line providers (e.g., primary care) in addressing the needs of OEF/OIF veterans with combat related PTSD and alcohol misuse. PUBLIC HEALTH RELEVANCE: Patients with PTSD-alcohol dependence are more costly to the VA health care system, as they have greater functional impairment, such as unemployment, increased violence and legal problems, family problems, and greater medical problems, such as HIV infection. Developing early interventions or improving existing treatments are dependent on our understanding of the processes by which PTSD and alcohol use inter-relate. Ultimately, better understanding of the etiology of alcohol use-PTSD comorbidity and improved treatments may lead to significant health care cost savings and improved public health for veterans.